By definition, all-wheel-drive (AWD) vehicles are those in which every wheel, or every set of wheels located on or sharing the same axis or axle, is provided with a separate motor. Since the use of several motors leads to a significant increase in power consumption, the most widely used in practice are the so-called hybrid vehicles employing at least one combination of an electric motor and a generator powered by an organic fuel. Technical solutions known from the prior art include an AWD vehicle with electric power supply from a liquid or gas turbine (U.S. Pat. No. 6,213,234, “Vehicle Powered By a Fuel Cell/Gas Turbine Combination”), a hybrid system employing a turbine engine (U.S. Pat. No. 5,762,156, “Hybrid Electric Propulsion System Using a Dual Shaft Turbine Engine”), a hybrid electric-motor drive (U.S. Pat. No. 5,765,656, “Hybrid Electric Motor Vehicle Drive”), and an electric drive system (U.S. Pat. No. 5,764,283, “Electric Propulsion System For a Vehicle”), among others.
All these disclosures relate to transport vehicles employing more than one electric motor, and some of them employ a separate motor for each wheel. In all cases, the vehicles are provided with at least two sources of power supply to the electric motors: a gas or liquid turbine and an electric accumulator or battery. The turbine operates as a normal electricity generator and powers the electric motors or charges the battery. The schemes of connecting the sources of power to the electric motors can be different. For example, an electric-motor car disclosed in U.S. Pat. No. 3,447,537 is equipped with a gas turbine, which acts as a generator for supplying power to electric motors driving each wheel. In one possible variant, the motors are powered from electric batteries, which in turn are charged from the generator.
In all the above devices, torque is transferred from the shaft of an electric motor to a wheel by means of a drive or a transmission mechanism. Another example is offered by patent application WO 2004/085186, which describes a vehicle comprising a distributed system of electric motors with a central controller. Each driving wheel is provided with a separate motor and a mechanical transmission. The proposed device can employ electric motors of various types, depending on the power source and the required characteristics. In particular, the vehicle can be supplied with power from a turbine generator and/or electric batteries. The motion of this vehicle is controlled by a complicated system, which synchronizes the electric motors and switches the transmission mechanisms.
Other examples and variants of AWD vehicles, transmission mechanisms, and control systems for electric motors and transmission have been described in U.S. patent applications 2003/0019674, U.S. 2003/0234124 and U.S. 2004/0176203.
These known AWD vehicles use mechanical drives to transfer the torque from the shaft of an electric motor to a wheel, and use mechanical transmission mechanisms to change the velocity of motion. This approach complicates the design and reduces the reliability of the system of control and synchronization of separate motors. Therefore the reliability of the whole vehicle is reduced.
Also known from the prior art is a gearless (direct-drive) motor-in-wheel (motor-wheel), whereby the wheel rotation is caused directly by the electromagnetic interaction of the magnetic systems of a stator and a rotor. Such systems, involving no mechanical drives and transmission mechanisms, offer promising technical solutions for transport vehicles.
One built-in motor known in the prior art (WO 93/08999 A1, 13.05.93) comprises two main parts: an immobile stator, mounted on an axis and provided with a magnetic conductor and a set of uniformly arranged permanent magnets, and a mobile rotor bearing a rim and containing at least two groups of electromagnets. A collector/distributor is mounted on the stator and provided with current-conducting plates connected to a dc current source. Said rotor bears current collectors which make electrical contact with the plates of the collector distributor.
Said motor-wheel can be implemented in several modifications and variants (U.S. Pat. No. 6,384,496 B1, 07.05.2002; U.S. Pat. No. 6,617,746 B1, 09.09.2003; Russian Patent 2,129,965 C1, 10.05.1999; Russian Patent No. 2,172,261 C1, 20.08.2001). Advantages of this design are the absence of a reducing gear, the use of low-voltage power sources, absence of supplementary electronic circuits, the possibility of energy recuperation, and relatively small size and weight characteristics. By combining the main elements of said motor-wheel with auxiliary elements, it is possible to create a variety of analogous devices retaining all the advantages of the motor-wheel.
However, the aforementioned motor-wheel and its analogs still have some disadvantages, the main of these being the need for large start and transient currents in the course of starting and accelerating the vehicle. This leads to rapid degradation and a decrease in the working life of storage batteries and to unfavourable thermal regimes. Another drawback is a low efficiency of the use and recovery of electric energy. Finally, said motor-wheels are characterized by relatively low torque, which considerably reduces the field of their possible practical applications.
Another motor employing a resonance scheme, which reduces the aforementioned disadvantages, has been described in the patent application WO 2004/091957 A1, 28.10.2004. Said motor contains an even number of electromagnets arranged in pairs, one opposite to another, with the terminals of opposite coils shunted by capacitors forming resonance circuits. The number (n) of permanent magnets in the stator and the number (m) of electromagnets (and resonance circuits) in the rotor are selected so as to obey the relations n=10+4k, and m=2+k, where k is an arbitrary integer (k=0, 1, 2, . . . ). For the proposed arrangement of magnets and the adopted scheme of commutation, these relations provide for a resonance of currents in the coils of the opposite electromagnets, which decreases the voltage jumps (and the energy consumption) in the start-up and acceleration regimes and improves dynamic characteristics of the motor. However, since the resonance of currents takes place only at a certain frequency of rotation, the optimum regime of motion of a vehicle employing said motor-wheel corresponds to a certain preset velocity (or a velocity interval).